1. Field of the Invention
The present invention relates to an intraocular implant (or artificial substitute lens) having on its surface a coating layer.
2. Related Background Art
Cataracts have been hitherto treated by surgery to deliver a lens having turned opaque and insert an artificial lens into the lenticular capsule, and recovering vision after the surgery. At present, such an intraocular implant is prevailingly used in the "in-the-bag system" which is considered to cause less complication that may accompany implantation, i.e., a system in which the intraocular implant is inserted into the "lenticular capsule".
As materials for such intraocular implants, polymethyl methacrylate is mainly used, and on the other hand, as materials for a lens support member called "haptic", polymethyl methacrylate, polyvinylidene fluoride or the like is used.
The surfaces of intraocular implants are required to be hydrophilic in order to prevent corneal cells from being damaged or improve a lens fitted feeling, and methods hitherto known as means for making the surfaces of intraocular implants hydrophilic include a method in which the surface of an intraocular implant is subjected to a plasma treatment, or a method in which a hydrophilic coating is formed on the surface of an intraocular implant by plasma polymerization using monomers of a nitro compound represented by the general formula R-NO.sub.2 (R is a hydrocarbon).
The method in which &he surface of an intraocular implant is subjected to a plasma treatment, which is a method comprising exposing the surface of an intraocular implant to oxygen plasma or nitrogen plasma to make its surface hydrophilic, has the following disadvantage. That is to say, the plasma treatment can achieve a uniform surface treatment with difficulty, and also may cause a deterioration with time wherein the hydrophilic nature becomes poor as time lapses. Hence, this method is not suited for the surface treatment& of intraocular implants which are required to be fitted for a long time.
The coating or film formed by plasma polymerization of the R-NO.sub.2 monomers can retain a superior hydrophilic nature, but a small discharge output applied in carrying out the polymerization may bring about an insufficient cross-linkage of the coating formed, resulting in an water-soluble film. Accordingly, a high discharge output is required for the formation of a non-water soluble film, and this necessarily limits film formation conditions to a such w high discharge output may also cause a slight opaqueness on the surface of the intraocular implant narrower scope. The film formation carried out at because of the plasma, which is unsuitable for the intraocular implant.
Other methods for making the surfaces of intraocular implants hydrophilic include dipping and graft polymerization utilizing ultraviolet rays, both of which, however, are accompanied with deterioration with time, and there has been a problem in stability.
On the other hand, the surfaces of intraocular implants are required to be capable of absorbing ultraviolet rays, harmful to retinas. For this purpose, U.S. Pat. No. 4,312,575, for example, discloses that a coloring substance may be included into the intraocular implant so that this coloring substance can absorb ultraviolet rays.
However inclusion of the ultraviolet absorbing substance into an intraocular implant lens substrate has caused the problem that the mechanical strength of the intraocular implant is lowered.